1. Field of the Invention
The present invention relates to an image format conversion system, and more particularly to a three-dimensional de-interlacing method and apparatus for converting an interlaced scan format into a progressive scan format.
2. Description of the Related Art
Generally, in the MPEG-2 standard, there are two scan formats: an interlaced scan format and a progressive scan format. In an encoder (not shown) and a decoder, situations can arise where it is necessary to convert an interlaced scan format video signal into a progressive scan format video signal. Such a scan format conversion is referred to as de-interlacing or Interlaced-to-Progressive Conversion (IPC).
FIG. 1 is a flow chart illustrating a conventional three-dimensional de-interlacing method. All operations for de-interlacing are generally performed on each pixel unit of an image field of an interlaced image frame. For example, it is assumed that IPC is performed at a position (i, j) of an n-th field, as shown in FIG. 2. In this case, a pixel at the position (i, j) of the n-th field is referred to as Yn(i, j).
At operation 112, image signals corresponding to the n-th field to be subjected to IPC and preceding and succeeding fields ((n−1)-th and (n+1)-th fields) of the n-th field are input. Subsequently, as shown in FIG. 2, at operation 114, a difference value Dmotion between the pixel of the (n−1)-th field and the pixel of the (n+1)-th field is calculated. Conventionally, the difference value Dmotion between the pixels is determined from pixels Yn−1(i, j) and Yn+1(i, j) located at the preceding and succeeding positions of Yn(i, j) and the pixels Yn−1(i, j+1), Yn−1(i, j+1), Yn+1(i,j−1) and Yn+1(i, j+1) located at the horizontally left and right positions of the pixels Yn−1(i, j) and Yn+1(i, j), using the following Equation 1.
                              D          motion                =                              1            3                    ⁢                                    ∑                              k                =                                  -                  1                                            1                        ⁢                                                                                              Y                                          n                      -                      1                                                        ⁡                                      (                                          i                      ,                                              j                        +                        k                                                              )                                                  -                                                      Y                                          n                      +                      1                                                        ⁡                                      (                                          i                      ,                                              j                        +                        k                                                              )                                                                                                                        (        1        )            
Subsequently, at operation 116, the difference value Dmotion is compared with a predetermined threshold value T. If the difference value Dmotion is greater than the predetermined threshold value T, at operation 118, it is considered that the pixel Yn(i, j) has moved and accordingly a motion index value Mn(i, j) is determined as “1”. On the other hand, if the difference value Dmotion is smaller than the threshold value T, at operation 122, it is considered that the pixel Yn(i, j) has not moved and accordingly the motion index value Mn(i, j) is determined as “0”.
In operation 124, it is determined whether the motion pixel values have been found for all the pixels in the n-th field to be subjected to IPC. Subsequently, if determined, at operation 124, that the motion index values for all the pixels in the n-th field to be subjected to IPC have been determined, at operation 126, a mode value M of each pixel in the nth field is finally determined using a motion index value of a pixel in the n-th field Yn(i, j), and using the motion index values of the pixels at the horizontally left and right positions (e.g., the pixels Yn(i, j±1)) of the pixel Yn(i, j). That is, as shown in FIG. 3, for example, the mode value M of Yn(i, j) is calculated using Equation 2 below.
                    M        =                                            ∑                                                k                  =                                      -                    1                                                  ,                                  +                  1                                                      ⁢                                          M                                  n                  -                  1                                            ⁡                              (                                                      i                    +                    k                                    ,                  j                                )                                              +                                    ∑                                                k                  =                                      -                    1                                                  ,                0                ,                                  +                  1                                                      ⁢                                          M                n                            ⁡                              (                                  i                  ,                                      j                    +                    k                                                  )                                                                        (        2        )            
In operation 128, if the mode value M of Yn(i, j) is “0”, it is determined that Yn(i, j) is in a stop mode. On the other hand, if the mode value M of Yn(i, j) is not “0”, it is determined that Yn(i, j) is in a motion mode. Subsequently, if determined at operation 128 that the mode value M of Yn(i, j) is in the stop mode, at operation 132, a pixel value is output to which a temporal interpolation method is applied using an average of two temporally adjacent pixels. On the other hand, if determined at operation 128 that the mode value M of Yn(i, j) is in the motion mode, at operation 134, a pixel value is output to which a spatial interpolation method is applied using an edge direction value. Subsequently, at operation 136, the IPC is completed on all pixels of the n-th field to be subject to IPC and the same process is performed on the next field.
However, conventionally, as shown in FIG. 1 operation 126, only the motion information of three pixels (i.e., a current pixel and two pixels at the horizontally left and right positions of the current pixel) are used to determine the motion index value. Therefore, at operation 114, sufficient motion information may not be reflected. In particular, the conventional IPC method cannot provide a robust threshold value T to detect images having a few motions as well as images having many motions, because sufficient motion information is not reflected at operation 114.